can you fix thick gaps in black printing

Hi,

This is for an HP Officejet Pro L7500.

There are thick gaps in the black printing (see Print Quality Diagnostics Page below).

I have tried cleaning the printheads, realignment, calibrating linefeed: no improvement.

I use only HP cartridges.

• Is this something that can be fixed by replacing the printheads?
• Do I need to take the printer to an HP repair shop?
• Is it fixable at all?

Thanks - Tzvi.